They believe the ringleader is a middle-aged woman, who was arrested at her home in Eccles yesterday.

She was said to live a luxury lifestyle, and her Aston Martin sports car was seized.

Police first became aware of the gang at the end of last year after parcels which were being sent through the post were intercepted by other forces, and substances inside were found to be illegal drugs coming from the North West.

Chief Supt David Hull, from Bolton police, said: “Cracking down on drugs in our communities is a big priority for GMP and I hope today’s operation show communities we are committed to this.

“Drugs wreck lives and the crime associated with the causes misery to the whole community — so we do everything possible to find out who is responsible and put them before the courts.”

Det Supt Jason Hudson, from the Titan operation, said: “We will now be looking at the customers of the website, wide-mouth-frogs.com, which was run from the unit in Farnworth, and where the drugs have been distributed to.”

He warned buyers that claiming that they thought the drugs were legal is not a defence if it turns out they are in possession of or supplying illegal drugs.

Mephedrone is a class B drug, but the drugs being sold online also included class A and C drugs.

Users are being warned that their effect on people’s health is not fully known.

Colin Tyrie, a substance misuse health adviser, said: “Mephedrone, along with some of the other new synthetic drugs, appears to be overtaking cocaine and ecstasy as the ‘club drugs’ or white powder drugs often referred to as bubble, magic, M-cat, amongst numerous other names for what are often blends of synthetic compounds produced to mimic illegal drugs like cocaine and ecstasy.

“Users will often snort the drugs, or take them in capsules, alongside alcohol and other drugs.”

Mr Tyrie added: “The risks of combining drugs and alcohol are often difficult to predict.”

A woman living in Valdene Drive, near the industrial unit, who asked not to be named, said: “I saw police there wearing white suits and masks and carrying things.

“It’s very scary. There were police everywhere.”

Another woman said: “I had no idea what they were doing. It makes me very worried that something so serious has been going on there.”

Four men and five woman aged between 21 and 62 were arrested on suspicion of the supplying drugs and money laundering. A 48-year-old man was arrested on suspicion of growing cannabis and two men, aged 29 and 30, were arrested on suspicion of drug dealing.